GB2035332A - Stabilized polymers - Google Patents

Abstract

Polymers which would otherwise be subject to degradation by the effect of oxygen and/or another atmospheric agent, have incorporated therein as a stabilizer a nickel pyrrolidine dithiocarboxylate of the following general formula:- <IMAGE> wherein each of R<1>, R<2>, R<3>, R<4>, R<5>, R<6>, R<7> and R<8>, which can be the same or different, is a hydrogen atom or an alkyl group.

Description

SPECIFICATION Stabilized polymers This invention relates to the stabilization of polymers, for instance thermoplastic polymers, which would otherwise be subject to degradation by the effect of oxygen and/or another atmospheric agent.

According to the present invention there is provided a stabilized polymer comprising a polymer and, incorporated therein as a stabilizer against oxygen or another atmospheric agent, a nickel pyrrolidine dithiocarboxylate having the following general formula:

wherein each of R1, R2, R3, R4, RB, R6, R7 and R8, which can be the same or different, is a hydrogen atom or an aikyl group.

Preferably at least two, and more preferably at least four, of the radicals R1 to RB are alkyl radicals.

More preferably R1, R3, R7 and R8 are alkyl radicals and R2, R4, R5 and RB are hydrogen atoms.

The radical R3 may, in this case, be a branched alkyl radical.

A preferred aspect of the present invention provides a stabilized polymer comprising a polymer and, incorporated therein as a stabilizer against oxygen or another atmospheric agent, a nickel tetralkyl pyrrolidine dithiocarboxylate having the following general formula:

wherein each of R1, R7, R8, R9, and R10, which are the same or different, is an alkyl radical.

In this case, preferably each of R1, R7, R8, R9 and R10 is a methyl radical.

The polymers which can be stabilised in accordance with the present invention are, for example, polyolefins (for instance polyethylene, polypropylene or polystyrene), vinyl polymers and acrylic polymers.

The stabilizing compounds are incorporated in the polymer by conventional methods, but should be added in the smallest effective quantity both for economical reasons and in order not to alter other characteristics of the resultant polymer, such as optical or mechanical properties, or colour.

The quanitity of stabilizer added is preferably up to 0.5% by weight of the polymer.

The present invention also provides a process for stabilizing a polymer, by incorporating therein a nickel pyrrolidine thiocarboxylate stabilizer.

By means of the present invention, substantial stabilization results are obtained at low addition levels, thus leading to considerable economy and safeguarding the characteristics of the final product.

By way of example, a description is now given of the synthesis of nickel 2,5,5-trimethyl-3-isopropyl pyrrolidine-dithiocarboxylate, and its use in stabilising polypropylene.

Example Part 1: Preparation of 2, 5,5-trimethyl-3-isopropylidene- 1-pyrrolidine.

This was prepared in accordance with the Ritter and Mayers method (J.O.C. 23 (1958)-1918). 450 Grams of 96% H2SO4were placed in a 1 litre flask fitted with a thermometer, dropping funnel and an efficient stirrer.

Then 70 cc of CH3CN were added through the dropping funnel at a rate such that the temperature of the reaction mixture did not exceed 5-6"C.

After the acetonitrile had been added, 170 g of 2,5-dimethyl-hexane-2,5-diol were added in small portions, while maintaining the temperature of the reaction mixture below 10"C.

After the 2,5-dimethyl-hexane-2,5-diol had been added, the mixture was stirred at a temperature of 10-15"C for a further hour, then made alkaline with a concentrated NaOH solution, and extracted several times with diethyl ether. The organic extracts were combined, dried over NaOH and distilled.

The desired product was obtained in a yield of 75% (B.P. 78 - 79"C at 14 mm Hg).

Part 2: Preparation of 2,5,5-trim eth yl-3-isoprop yip yrrolidine This product was prepared by dissolving the corresponding 3-isopropylidine-pyrrolidine, prepared as described in Part 1, in glacial acetic acid and hydrogenating at a temperature of 30 - 40"C under a hydrogen pressure of less than 15 kg/cm2, using palladuim on carbon (Pd/C) as catalyst.

At the end of the reaction, the reaction liquid was filtered to remove the catalyst, neutralised with NaOH and extracted several times with diethyl ether.

The ethereal extracts were combined, dried and distilled.

The liquid product was colourless and of unpleasant odour, and had a B.P. of 58-60"C at 9 mm Hg, and a nd25 1.438 (read.nd22 1.4392) The l.R. spectrum showed the characteristic bands of the N-H group, and N.M.R. analysis enabled the structure of the product to be determined.

Elemental analysis: C% H% N% experimental 78 13.2 8.7 theoretical 77.5 13.5 9 Part 3: Preparation of nickel 2,5,5-trimethyl-3-isopropyl-pyrrolidine-dithiocarboxylate 10 Grams of 2,5,5-trimethyl-3-isopropylpyrrolidine were dissolved in a flask containing 4 cc of carbon disulphide and 10 cc of ethyl alcohol.

The reaction mixture was kept stirred at 50"C for 20 minutes.

A solution of 7 g of NiCl2.6H2O in 50 cc of ethyl alcohol was then added. There was an immediate precipitation of a green crystalline product which was separated from the mother liquor and washed abundantly with ethyl alcohol.

The solid obtained had a melting point of 263-265"C.

The elemental analysis corresponded practically to the theoretical: C% H% N% experimental 50.2 7.5 5.2 11.8 24.3 theoretical 50.9 7.7 5.2 11.2 24.7 Part 4: UVstabilisation ofpolypropylene Various quantities of the product from Part 3 of the Example were added to a general purpose polypropylene already mixed with the normal stabilisers and process ingredients. Mixing was carried out by the usual method for incorporating stabilisers in polyolefins (e.g. 180" cylinder mixes).

Plates of 0.5 mm thickness were prepared, and were exposed in a weatherometer to two arc lamps having emission maxima at 3,600, 3,850 and 4,200 .

The resistance of the polypropylene to the UV exposure was evaluated by viscosity measurements (Melt Flow Index = MFI) as prescribed by ASTM D 1238, after various exposure times.

The results of the tests for polypropylene containing no stabilizer and for polypropylene containing either the product of Part 3 of the Example, or for comparative purposes, one or other of two commercial stabilisers, namely UV 531, a benzophenone derivative, and UV 770, a multisubstituted amine, are given in the following table: MFI MFI MFI initial after 400 after 800 hours hours polypropylene as such 3.8 6 15 polypropylene with 0.5% UV 531 4 5 6 " " 0.5% UV 770 4 4.5 5 " " 0.5% prod.Ex 3.7 3.4 3.5 " 0.3% " " prod.Ex 3.7 3.4 3.5 The greater stabilising effect of the product under examination relative to the commercial products is apparent, even at a lower concentration.

Claims (10)

1. A stabilized polymer comprising a polymer and, incorporated therein as a stabilizer against oxygen or another atmospheric agent, a nickel pyrrolidine dithiocarboxylate having the following general formula:

wherein each of R', R2, R3, R4, R5, R6, R7 and RB, which can be the same or different, is a hydrogen atom or an alkyl group.

2. A stabilized polymer according to Claim 1, wherein at least two of R1 to R8 are alkyl radicals.

3. A stabilized polymer according to Claim 1, wherein at least four of R1 to R8 are alkyl radicals.

4. A stabilized polymer according to Claim 1, wherein R1, R3, R7 and R8 are alkyl radicals and R2, R4, R5 and R6 are hydrogen atoms.

5. A stabilized polymer according to Claim 4, wherein R3 is a branched alkyl radical.

6. A stabilized polymer comprising a polymer and, incorporated therein as a stabilizer against oxygen or another atmospheric agent, a nickel tetra alkyl pyrrolidine dithiocarboxylate having the following general formula:

wherein each of R1, R7, R8, R9 and R10, which are the same or different, is an alkyl radical.

7. Astabilized polymer according to Claim 6, wherein each of R1, R7, R8, R9 and R10 is a methyl radical.

8. A stabilized polymer according to any preceding claim, in which the stabilizer is present in a quantity of up to 0.5% by weight of the polyer.

9. A stabilized polymer according to any preceding claim, wherein the polymer being stabilized is a polyolefin, a vinyl polymer or an acrylic polymer.

10. A process for stabilizing a polymer which comprises incorporating therein a stabilizer as defined in any one of Claims 1 to 7.